(a) Field of the Invention
The present invention relates to a mobile communication system, and in particular, it relates to a method and device for estimating a timing error and a frequency offset in a mobile communication system.
(b) Description of the Related Art
As the services such as the real-time Internet and VoIP have been provided according to users' various requests, techniques for supporting high data rates have been developed. The OFDM (the Orthogonal Frequency Division Modulation) highlighted as the most useful technique among the next generation mobile communication techniques has been adopted as the wireless LAN standards and European digital audio and video broadcasting standards.
A major method for realizing high data rates is to improve link process throughputs and network capacity. A method for improving the throughput is the MIMO (multiple-input multiple-output) technique, in which a plurality of antennas is installed in a transmitter and a receiver, the transmitter transmits data to the receiver through multipaths, the receiver receives and detects signals transmitted through the respective path, and thus, the throughput is substantially increased because of the antennas. The MIMO technique is basically divided into two groups, that is, the STC (space time coding) and the SDM (space division multiplexing).
To satisfy the requirement for high data rates, the OFDM-MIMO system provided by combining the OFDM and the MIMO has been used. To improve the OFDM-MIMO system performance, time and frequency synchronization is required. A frequency offset is generated because of mismatching between oscillators of the transmitter and the receiver and the Doppler effect, and the frequency offset changes the phase of received signals to thus deteriorate decoding performance of the receiver. Particularly, in the multi-carrier using OFDM, the symbol is detected for each subchannel, and hence, when a frequency offset is generated, the orthogonality between the subcarrier frequencies is not maintained so that interference between adjacent subchannels is generated. The interference is called ICI (inter-carrier-interference). Also, a timing offset is generated, which disturbs orthogonality between the received subcarriers.
Accordingly, various techniques for estimating and eliminating the frequency offset and the timing offset generated by the receiver have been proposed. Conventional techniques generally use the DA (data-aided) algorithms having synchronization information and the NDA (non data-aided) feedforward estimation structures having statistics of received signals.
The signals received by the receiver are influenced by ISI because of a multipath channel before undergoing a FFT process. However, the prior arts fail to estimate accurate timing errors and frequency offsets since they do not consider the ISI effects.